How can the Diamondbacks fix Zac Gallen’s pitching struggles?

The decline appears to be driven by multiple factors working together. Opposing hitters have become increasingly comfortable against Gallen’s sequencing, while the margin for error that once made his arsenal elite has nearly disappeared. His fastball velocity has remained around 93 mph throughout his career, eliminating the easy explanation of declining arm strength. Instead, the deterioration has shown up in the finer details that separate good pitchers from great ones, and that is why Gallen is sitting with a league-worst 6.15 ERA.

Gallen built his career on exceptional pitch tunneling, using tight differences in movement and spin to make every offering look identical until the final moments. Small reductions in spin rate and movement have made his breaking pitches easier to identify, particularly his knuckle curve, which no longer generates the swing-and-miss numbers it once did. Hitters aren’t chasing. They’re waiting for favorable counts and punishing mistakes. That creates a dangerous cycle. As hitters become more selective, Gallen is forced into predictable situations, making his chess-match approach less effective than it once was.

The solution isn’t necessarily finding more velocity; it’s reinvention. Many successful veterans have redesigned their arsenals during the second half of their careers by simplifying their approach, altering pitch shapes, and prioritizing execution over perfect sequencing. Arizona’s coaching staff may need to guide Gallen through that same transition before the problem becomes irreversible. Pitchers often decline in their mid-to-late 30s. What’s alarming is that Gallen’s transformation from Cy Young candidate to replacement-level production has happened before turning 31. If the Diamondbacks hope to remain contenders, fixing these issues must be a priority for them going forward.